1,720,966 research outputs found
Portable Device for Rail Bending and Torsion measurement
No full textA portable device for assessing rail bending and torsion as well as the relative wheel-rail position was designed and tested. The main requirement for this device is that its first eigenfrequency should be well above the first bending eigenfrequency of the rail in order not to dynamically amplify rail bending motions. Thus, a minimum target frequency of 100Hz is set. Another requirement is to design a device that could be easily mounted on different track sections in order to assess also the influence of vehicle type and speed. Thus, a portable device based on laser sensors was produced that does not require any operations on the rails (contactless sensors) and allows to place the sensors at a reasonable distance from both the rail and the passing by wheel. Tests were performed on a dedicated test track in Czech Republic both at low speed (20km/h on a 150m radius curve) and at medium speed (90km/h on a 600m radius curve) with two axle and four axle wagons. Installation was extremely easy and acquired signals were post-elaborated to assess rail vertical and lateral bending as well as torsion
Influence of electrical load on the dynamics of a piezoelectric energy harvester
No full textThe performance of a piezoelectric energy harvester is closely related to the narrow
range of frequencies in which it can operate efficiently. In a bimorph, the electrical load
influences the dynamic response and therefore the natural frequency of the structure. This research
focuses on the relationship between the impedance of the electrical circuit connected to
the bimorph and the mechanical dynamics of the system as a whole. Some preliminary considerations
are carried out using a coupled analytical model. Then experimental tests are performed
in order to validate the results and to define the optimal conditions for the energy conversion
Tribometro e metodo per misurare il coefficiente di attrito radente
No full textUn tribometro (1) per misurare l’attrito radente di un provino di materiale da testare su una superficie di scorrimento, comprende una struttura di supporto fissa (5) appoggiata a terra ed una struttura di supporto rotante (6), la quale è supportata in rotazione attorno ad un asse di rotazione (Y-Y) unitamente a contrapposti porta-provini (2), detti porta-provini (2) essendo collegati solidali in rotazione a detta struttura di supporto rotante (6) ad una prefissata distanza (D) da detto asse di rotazione (Y-Y)
Design of a wireless sensor powered by a piezoelectric energy harvester
No full textSensor nodes are innovative devices that can perform measurements on a large scale and communicate over a network. One of the most significant problems regarding the sensor nodes is how to supply power to a large number of devices. For this reason, they greatly benefit from energy harvesting techniques which can provide energy recovered directly from the environment. A study of the design and the modeling of an autonomous sensor node, powered by a vibrational piezoelectric harvester, is reported here. Subject of the first part of the analysis is a piezoelectric bimorph: an analytical model is proposed in order to estimate the performance, giving particular attention to the optimal mechanical and electrical parameters. The model is then validated through experimental tests, assuming different kinds of real scenarios. Then the results are used to design a device that can benefit from this harvester. In particular a wireless sensor node is developed, for which the energy scavenging ensures energy autonomy and long-term operability. Thanks to a particular harvesting circuit and opportune algorithms for energy management, this system is able to extract energy from vibrations and store it into capacitors. The embedded accelerometer and a wireless module make this device ideal for Structure Health Monitoring purposes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Smart sensor for detection of derailment on freight trains
No full textIn this paper a sensor node able to monitor the growth of a crack in a wheelset, by means of axle box acceleration measurements, is described and the first results of experimental field tests are presented. The sensor node is equipped with a wireless transmission system and a bimorph piezoelectric energy harvester. Moreover, the node is inserted in a specific suspension system, which allows the measurement of low frequency accelerations (around wheel revolution and its first multiples) and amplifies the energy recovered by the harvester. The first tests on a freight convoy along a traditional Italian railway line show that the designed sensor node is able to acquire, analyse and transmit data with a frequency which depends on the power needed by the operation cycle
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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